Third Generation (3G) Wireless Networks
3G wireless networks may interface with external networks such as the internet. Third generation (3G) wireless networks have a General Packet Radio Service (GPRS) core network that facilitates the transmission of Internet Protocol (IP) packets between the 3G wireless network and the internet. The GPRS core network may use a GPRS tunneling protocol that allows users of the 3G wireless network to be coupled to external networks while moving from one location to the other. The GPRS may include various components such as the Service GPRS Support Node (SGSN) and Gateway GPRS Support node (GGSN). The SGSN can interface with a Radio Network Controller (RNC).
The functionality of the different 3G wireless network components is known in the art and defined in various known standards. One non-limiting explanation relating to the SGSN, the RNC and the GGSN can be found in www.wikipedia.org.
Gateway GPRS Support Node (GGSN)—The Gateway GPRS Support Node (GGSN) is a main component of the GPRS network. The GGSN is responsible for the interworking between the GPRS network and external packet switched networks, like the Internet and X.25 networks. From an external network's point of view, the GGSN is a router to a sub-network, because the GGSN ‘hides’ the GPRS infrastructure from the external network.
When the GGSN receives data addressed to a specific user, it checks if the user is active. If it is, the GGSN forwards the data to the SGSN serving the mobile user, but if the mobile user is inactive, the data is discarded. On the other hand, mobile-originated packets are routed to the right network by the GGSN. The GGSN is the anchor point that enables the mobility of the user terminal in the GPRS/UMTS networks. In essence, it carries out the role in GPRS equivalent to the Home Agent in Mobile IP. It maintains routing necessary to tunnel the Protocol Data Units (PDUs) to the SGSN that service a particular MS (Mobile Station).
The GGSN converts the GPRS packets coming from the SGSN into the appropriate packet data protocol (PDP) format (e.g., IP or X.25) and sends them out on the corresponding packet data network. In the other direction, PDP addresses of incoming data packets are converted to the GSM address of the destination user. The readdressed packets are sent to the responsible SGSN. For this purpose, the GGSN stores the current SGSN address of the user and his or her profile in its location register. The GGSN is responsible for IP address assignment and is the default router for the coupled user equipment (UE). The GGSN also performs authentication and charging functions. Other functions include subscriber screening, IP Pool management and address mapping, QoS and PDP context enforcement. With LTE scenario the GGSN functionality moves to SAE gateway (with SGSN functionality working in MME).
Serving GPRS Support Node (SGSN)—a Serving GPRS Support Node (SGSN) is responsible for the delivery of data packets from and to the mobile stations within its geographical service area. Its tasks include packet routing and transfer, mobility management (attach/detach and location management), logical link management, and authentication and charging functions. The location register of the SGSN stores location information (e.g., current cell, current VLR) and user profiles (e.g., IMSI, address or addresses) used in the packet data network) of all GPRS users registered with this SGSN components.
Radio Network Controller (RNC)—the RNC is a governing element in the UMTS radio access network (UTRAN) and is responsible for controlling the Node Bs that are coupled to it. The RNC carries out radio resource management, some of the mobility management functions and is the point where encryption is done before user data is sent to and from the mobile. The RNC connects to the Circuit Switched Core Network through Media Gateway (MGW) and to the SGSN (Serving GPRS Support Node) in the Packet Switched Core Network. The logical connections between the network elements are known as interfaces.
The interface between the RNC and the Circuit Switched Core Network (CS-CN) is called Iu-CS and between the RNC and the Packet Switched Core Network is called IuPS. Other interfaces include Iub (between the RNC and the Node B) and Iur (between RNCs in the same network). Iu interfaces carry user traffic (such as voice or data) as well as control information Iur interface is mainly needed for soft handovers involving 2 RNCs though not required as the absence of Iur will cause these handovers to become hard handovers . . . ub, Iu and Iur protocols all carry both user data and signaling (that is, control plane).
Signaling protocol responsible for the control of the Node B by the RNC is called NBAP (Node-B Application Part). NBAP is subdivided into Common and Dedicated NBAP (C-NBAP and D-NBAP), where Common NBAP controls overall Node B functionality and Dedicated NBAP controls separate cells or sectors of the Node B. NBAP is carried over Iub. In order for NBAP to handle common and dedicated procedures, it is divided into: NodeB Control Port (NCP) which handles common NBAP procedures and Communication Control Port (CCP) which handles dedicated NBAP procedures. Control plane protocol for the transport layer is called ALCAP (Access Link Control Application Protocol).
Basic functionality of ALCAP is multiplexing of different users onto one AAL2 transmission path using channel IDs (CIDs). ALCAP is carried over Iub and Iu-CS interfaces. Signaling protocol responsible for communication between RNC and the core network is called RANAP (Radio Access Network Application Part), and is carried over Iu interface. Signaling protocol responsible for communications between RNCs is called RNSAP (Radio Network Subsystem Application Part) and is carried on the Iur interface.